A camera module (solid-state image pickup device) for use in a mobile phone or the like is a module integrally constituted by a solid-state image pickup element (CCD (charge-coupled device) or a CMOS (complementary metal-oxide semiconductor) sensor IC (integrated circuit)), an infrared filter, and a printed-circuit board having terminals, a lens, and a lens holder. Recently, in order to miniaturize a camera module, a process for manufacturing a miniature solid-state image pickup element has been developed. As the size of a camera module becomes smaller, fine dust (e.g., of not less than 25 μm) existing on the optical path causes an image defect. Such an image defect is caused when the shadow of dust on the optical path is projected as a black dot or a stain onto a shot image. It should be noted that the optical path of a camera module is indicated by a line connecting a lens with a light-receiving portion of a solid-state image pickup element.
Examples of the dust that causes such an image defect include dust having already adhered to a component of the camera module at the time of arrival of the component and dust generated in process of manufacture. It should be noted here that the dust having already adhered at the time of arrival is often formed from fine resin chips. Meanwhile, the dust generated in process of manufacture is often formed from metal. Such metal is generated by the abrasion of an apparatus for manufacturing (assembling) a camera module.
If the dust thus generated adheres onto the optical path, the dust can be removed at the time of shipping inspection included in a process for manufacturing a camera module. However, dust temporarily adhering to a portion other than the optical path cannot be removed at the time of shipping inspection; therefore, the camera module is shipped as a conforming article. For this reason, when the camera module thus shipped is shocked or vibrated during conveyance or transportation of the camera module, the temporarily-adhering dust moves and adheres onto the optical path. This causes an image defect at the place (user source, e.g., a camera-equipped mobile phone seller) to which the camera module has been shipped.
One of the conventional measures against such an image defect is to screen dust having already adhered to a component of a camera module at the time of delivery of the component. Moreover, depending on the extent to which the dust adheres, the dust is blown away with use of a air blower, washed away with use of ultrasonic waves, washed away with HFE (hydrofluoroether).
Meanwhile, in order to prevent dust generated in process of manufacture from adhering to a component of a camera module, an attempt to raise standards of cleanliness of a manufacturing line has been made. For example, manufacturing is performed in a clean room cut off from the outside world.
However, such an attempt requires facility investment, control of maintenance, manufacturing process maintenance (e.g., apparatus cleaning and component replacement), and the like. That is, the installation of a clean room, the investment in facilities for air circulation (e.g., air curtains, air circulators, filtration facilities, and cleaning facilities) and the like, and the control of maintenance of those facilities involve enormous cost. Moreover, as described above, even if dust is prevented from entering at the time of assembly of a camera module in a clean room, there is a possibility that dust is generated in the clean room. For this reason, the securement of standards of cleanliness in manufacturing processes is no longer sufficient to remove dust.
In view of this, each of Patent Documents 1 and 2 discloses a solid-state image pickup device that employs an adhesive material to catch dust that causes an image defect.
FIG. 20 is a cross-sectional view of the solid-state image pickup device of Patent Document 1. According to this arrangement, a space formed by a package 111, a solid-state image pickup element 112, and a sealing glass 114 (i.e., an inner wall surface of the package 111) is coated with an adhesive material 115. The adhesive material 115 catches dust 113 generated in the space.
Meanwhile, FIG. 21 is a cross-sectional view of the solid-state image pickup device of Patent Document 2. According to this arrangement, a charged film 230 is provided in a space 220 zoned by the inner side of a concave portion 218 of a lens holder 216 and a substrate 202. Furthermore, an adhesive material 234 is provided on the charged film 230 so as to be exposed to the space 220. The adhesive material 234 catches dust 232 sucked by the charged film 230 with electrostatic action.
Further, Patent Document 3 discloses a solid-state image pickup device that prevents dust from adhering to a solid-state image pickup element. FIG. 22 is a cross-sectional view of the solid-state image pickup device of Patent Document 3. According to this solid-state image pickup device, threads (including an inner thread 308 and an outer thread 324) for fastening a lens barrel 320 and a lens-barrel-attaching frame 322 together are formed outside of the lens-barrel-attaching frame 322. With this, dust generated by friction between the lens barrel 320 and the lens-barrel-attaching frame 322 at the time of adjusting focus by adjusting the distance between the lens barrel 320 and a solid-state image pickup element 327 can be prevented from adhering to the solid-state image pickup element 327.
However, the conventional arrangements are insufficient to take measures against dust and incapable of miniaturizing a solid-state image pickup device.
Specifically, as described above, the arrangement of Patent Document 1 employs the adhesive material 115, provided in the same space as the solid-state image pickup element 112, to catch dust. Meanwhile, the arrangement of Patent Document 2 employs the adhesive material 234 not only to simply catch dust, but also to catch dust sucked by the charged film 230.
However, the arrangement of Patent Document 1 cannot prevent dust from adhering onto a surface of the sealing glass 114 that lies on a line extending from the solid-state image pickup element 112. That is, the arrangement of Patent Document 1 cannot prevent dust from adhering onto the optical path. For this reason, the dust causes an image defect.
Further, the arrangement of Patent Document 2 employs the charged film 230 to suck dust. However, the charged film 230 is provided also in the optical path. For this reason, even if the adhesive material 234 is not provided in the optical path, dust is attracted toward the charged film 230 provided in the optical path. Moreover, the adhesive material 234 is not provided so as to face a lens unit 212. As a result, dust adheres onto both sides of the charged film 230 provided in the optical path. Thus, the arrangement of Patent Document 2 also cannot prevent dust from adhering onto the optical path, and therefore suffers from an image defect.
Moreover, the arrangement of Patent Document 2 suffers from such a problem that the static electricity with which dust is sucked causes a malfunction in the solid-state image pickup device 206 and such a problem that there is dust, such as metal dust, which cannot be sucked with static electricity.
Meanwhile, the arrangement of Patent Document 3 does not employ an adhesive material or static electricity as Patent Documents 1 and 2 do. Moreover, since dust is generated outside of the lens-barrel-attaching frame 322, no dust adheres to the solid-state image pickup element 327. However, the threads for fastening the lens barrel 320 and the lens-barrel-attaching frame 322 together need to be provided outside of the lens-barrel-attaching frame 322. This makes it necessary not only to provide a convex pedestal 325 on an outer circumferential surface of the lens-barrel-attaching frame 322 so that the convex pedestal 325 extends from the outer circumferential surface of the lens-barrel-attaching frame 322, but also to provide the lens barrel 320 with a second barrel 304 having the inner thread 308 provided on an inner surface thereof. This undesirably causes an increase in the size of the solid-state image pickup device of Patent Document 3.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 261158/1987 (Tokukaisho 62-261158; published on Nov. 13, 1987)
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 42230/2006 (Tokukai 2006-42230; published on Feb. 9, 2006)
[Patent Document 3]
Japanese Unexamined Patent Application Publication No. 06502/2007 (Tokukai 2007-06502; published on Jan. 11, 2007)